This invention relates to the design of a micromechanical device for spatially and temporally modulating an incident beam of light by diffraction. More particularly, this invention discloses an electromechanical conformal grating device having a support structure designed for improved optical efficiency and contrast.
Electromechanical spatial light modulators with a variety of designs have been used in applications such as display, optical processing, printing, optical data storage and spectroscopy. These modulators produce spatial variations in the phase and/or amplitude of an incident light beam using arrays of individually addressable devices.
One class of electromechanical spatial light modulators has devices with a periodic sequence of reflective elements that form electromechanical phase gratings. In such devices, the incident light beam is selectively reflected or diffracted into a number of discrete orders. Depending on the application, one or more of these diffracted orders may be collected and used by the optical system. Electromechanical phase gratings can be formed in metallized elastomer gels; see U.S. Pat. No. 4,626,920 issued Dec. 2, 1986 to Glenn, and U.S. Pat. No. 4,857,978 issued Aug. 15, 1989 to Goldburt et al. The electrodes below the elastomer are patterned so that the application of a voltage deforms the elastomer producing a nearly sinusoidal phase grating. These types of devices have been successfully used in color projection displays.
An electromechanical phase grating with a much faster response time can be made of suspended micromechanical ribbon elements, as described in U.S. Pat. No. 5,311,360 issued May 10, 1994, to Bloom et al. This device, also known as a grating light valve (GLV), can be fabricated with CMOS-like processes on silicon. Improvements in the device were later described by Bloom et al. that included: 1) patterned raised areas beneath the ribbons to minimize contact area to obviate stiction between the ribbons and the substrate, and 2) an alternative device design in which the spacing between ribbons was decreased and alternate ribbons were actuated to produce good contrast; see U.S. Pat. No. 5,459,610 issued Oct. 17, 1995. Bloom et al. also presented a method for fabricating the device; see U.S. Pat. No. 5,677,783 issued Oct. 14, 1997. With linear GLV arrays of this type, the diffraction direction is not perpendicular to the array direction, which increases the complexity of the optical system required for separation of the diffracted orders. Furthermore, the active region of the array is relatively narrow requiring good alignment of line illumination over the entire length of the array, typically to within 10-30 microns over a few centimeters of length. The line illumination then also needs to be very straight over the entire linear array.
There is a need therefore for a linear array of grating devices that has a large active region with the diffraction direction perpendicular to the array direction. Furthermore, the device must be able to diffract light efficiently into discrete orders while having high contrast and high speed. Additionally, the device fabrication must be compatible with CMOS-like processes.
The need is met according to the present invention by providing an electromechanical conformal grating device having a period A, that includes: an elongated ribbon element including a light reflective surface; a pair of end supports for supporting the elongated ribbon element at both ends over a substrate; an intermediate support; and means for applying a force to the elongated ribbon element to cause the element to deform between first and second operating states, where in the second operating state the elongated ribbon element mechanically conforms to the intermediate support forming a conformal grating having alternating raised and lowered portions, and wherein the length of the raised and lowered portions are substantially equal.